Mike,
The "alt key + 4 digit code" is strictly a windows device. You CAN use these fonts on your iMac (and should). There are two ways to do it. One: hold down the ctrl key, option key, shift key, and many combinations of the three and start pressing letters [guess and check]. Two: Go to system preferences, click "International" and the click the "Input Menu" tab. At the bottom of the window, make sure "Show input menu in menu bar" is checked. Then, from the scroll window, check the boxes for "Character Palette" and "Keyboard Viewer." Now, there should be an american flag in your menu bar. Click it to select either of the two above. Character Palette is a useful thing to have for those outlandish symbols like square root or greek letters. Keyboard Viewer is what you need. Opening that window will give you a view of your keyboard. Holding down alt, ctrl, shift, etc, will show you the characters that become accesible. Also, remember that this is different for each font, so use the pull down menu to find the one you need.
Hopefully this is clear enough. Let me know if you need any more help--sorry I'm so late.